The purposes of the proposed project are to determine how Tl loads its head with foreign DNA. This will be done by characterizing Tl mutants already available as to their ability to transduce and to isolate new mutants. In addition, the effect of various rec mutants of E. coli will be studied to determine their effect on transduction by Tl. The production of specialized Tl transducing particles for Bio plus will also be studied. Attempts will be made to isolate recombination mutants of Tl.